Liquid crystal displays are being used as displays of a broad spectrum of electronic apparatuses making use of their characteristics of being thin in shape and low in power consumption. For example, there are laptop type personal computers, displays for car navigation, personal digital assistants (PDAs), mobile phones, digital cameras, video cameras, and other electronic apparatuses using liquid crystal displays. Such liquid crystal displays include, roughly classified, transmission type liquid crystal displays controlling the passage and blocking of light from an internal light source referred to as a backlight by a liquid crystal panel to perform the display and reflection type displays for reflecting sunlight or other external light by a reflection plate or the like to control the passage and blocking of this reflected light by the liquid crystal panel and perform the display.
In a transmission type liquid crystal display, the backlight accounts for 50 percent or more of the total power consumption, so it is difficult to reduce the power consumption. Further, a transmission type liquid crystal display also has the problem that the display looks dark where the ambient light is bright, so the viewability is lowered. On the other hand, in a reflection type liquid crystal display, a backlight is not provided, so there is no problem of an increase of the power consumption, but there is also a problem that the viewability is sharply lowered when the ambient light is low.
In order to solve such problems of both of the transmission type and reflection type display devices, a dual reflection and transmission type liquid crystal display realizing both transmission type display and reflection type display by one liquid crystal panel has been proposed. This dual reflection and transmission type liquid crystal display performs the display by the reflection of the ambient light when the surroundings are bright, while performs the display by the light of the backlight when the surroundings are dark.
In a conventional dual reflection and transmission type liquid crystal display, however, though both transmission type display and reflection type display are provided, there were the problems that the luminance was insufficient and the viewability lower than the usual reflection type and the usual transmission type liquid crystal displays. Particularly, the conventional dual reflection and transmission type liquid crystal display employed a liquid crystal panel configuration stressing reflection display, so secured a wide area for the region for reflecting the ambient light and secured reflectance by sacrificing the transmission luminance.
For example, Japanese Examined Patent Publication No. 2955277 (Patent Document 1) discloses a dual reflection and transmission type liquid crystal display. This liquid crystal display is predicated on a reflection liquid crystal display utilizing the reflected light of the ambient light and handles the sharp drop in the viewability when the ambient light is low.
However, a reflection and transmission type display device stressing the reflection type is small in appeal to people's tastes, so in the actual market, liquid crystal displays employing transmission type display as a main display system are used more often for PDAs, mobile phones, laptop type personal computers, displays for car navigation, digital cameras, video cameras, etc.
Further, Patent Document 1 mentions only color reproducibility as an item for improvement and does not describe anything about the luminance required for a liquid crystal display.
Further, Japanese Unexamined Patent Publication (Kokai) No. 2000-111902 (Patent Document 2) similarly discloses a liquid crystal display using reflection type display and transmission type display together. In this liquid crystal display, a window of a color filter for improving the luminance of the reflection portion is arranged over the entire reflection region. In the liquid crystal display according to Patent Document 2, the shape of the window is not explained, but when the reflection region is formed in a limited place, directivity of the reflected light with respect to the incident light easily occurs. Further, the minimum size of the window is not defined, therefore when transmission type display becomes the main display system, the reflection region cannot be reduced to the lowest limit.
Note that in a liquid crystal display, it is desirable to improve the viewability of the display both when used indoors and when used outdoors. For this reason, in a dual reflection and transmission type liquid crystal display, an improvement of the viewability is desirable for both of the case when it is used as the reflection type and the case when it is used as the transmission type. Particularly, as described above, in practice, most electronic apparatuses employ transmission type display as the main display system rather than reflection type display. Therefore it is desirable to improve the luminance of the transmission type display in a dual reflection and transmission type liquid crystal display.
On the other hand, along with the demands for improving the luminance of a transmission type display, it has been demanded to further increase the definition of liquid crystal displays.
For example, the liquid crystal displays used in PDAs, mobile phones, laptop type personal computers, displays for car navigation, digital cameras, video cameras, etc. have been conventionally made in the range from 100 ppi (pixel per inch) to 140 ppi. However, in order to prevent jagged edges of characters displayed and display images of the same quality as photographic images, there is a growing need for increasing the definition to 200 ppi or more.
Concerning increasing the definition to 200 ppi, due to the limits in design of liquid crystal pixels, for example the minimum width or pitch of signal lines and gate lines is not less than 5 μm, there are the disadvantages that the region which can be utilized for transmission type display for each pixel is reduced and the transmission type display luminance is reduced.
For example, by increasing the luminance of the backlight used in the transmission type, the above high definition can be realized while securing a high transmission type display luminance. As explained above, however, this means the increase of the luminance of the backlight, so the power consumption of the liquid crystal display increases. Therefore, this becomes a defect for a liquid crystal display boasting low power consumption.